Apparatus for the performance of chemical reactions, such as roasting, calcining, or the like



C. P. DEBUCH APPARATUS FOR THE PERFORMANCE OF CHEMICAL REACTIONS, SUCH AS ROA S'IING, CALCINING OR THE LIKE Origmal Filed Aug. 28, 28heets-Sheet 1 I Oct. 29, 1935.

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SUCH AS ROASTING, CALCINING OR THE LIKE Original Filed Aug. 28, 1935 2 Sheets-Sheet 2 ikga .YQ vIIJ Patented a. 29, 1935 'U Nl'lED STATES-PATENT orrice n 2,019,391 I I APPARATUS FOR ,THE PERFORMANCE OF CHEMICAL REACTIONS, SUCH AS ROAST- ING, CALCINING, OR THE LIKE Carl Paul Debuch, Frankfort-on-the-Main, Germany, assignor to American Lurgi Corporation, New York, N. 1., a corporation of New York Original application August 28, 1983, SeriaiNo.

887,234. Divided and this application Septemher 4, 1984. Serial No. 742,662. In Germany August 14, 1930 8 m (Cl. 283-63) This invention relates to a process for the performance of chemical reactions, such as roasting, calcining 'or the like.

In processes for the performance of chemical reactions, in which the" material to be treated is passed througha heated reaction chamber, the said material is mostly-lacking in uniformity in respect to'its physical character. This is ardefect which attempts are made to rectify, in oer-- 6- tain cases, by previously classifying the material into different grain sizes, which are treated separately. In this connection, mention may be made of the calcination of lump magnesite in shaft furnaces, andof fine-grained magnesite in rotary-tube furnaces. 0n the same lines, special types of furnace (lump pyrites furnaces) and processes have been devised for roasting pyrites in the form of large lumps, and special furnaces (fine-pyrites furnaces) and processes for roasting the same ores when in a finely divided form.

The commercial term "fines, as applied to pyrites, comprises for example, all crushed pyrites with a grain size of up to 0.8 to 0.10 ms. Ac-

cording to the requirements of the purpose in view, the classification into grain sizes may, of course,'difier from that specified. Even in such fine-grained material, the several sizes difier in orzinc hlende, to calcination, asregards the splitting of! of carbon dioxide and water of hydration and also to a whole series of other proc- 4u, esses, such as the splitting of! of sulphur dioxide from gypsum or heavy spar, and the calcining or sintering of magnesite or the like.

The circumstance that in fine-grained material the finest grain is more reactive than the coarser,

has already been utilized invarious ways. Thus,

in' calcining magnesite, the crushed or ground material has been treated in a rotary-tube furnace, in such a manner as to produce both causticized and dead-burned, or sinteredmagnesiteat 50 one and the same time.- At a point where a working temperature of about 900 to 1000 was attained, the rotary-tube furnace was provided with holes through which the caustic magnesiteof uniform grain size if desired-was discharged.

as The bulk of the charge was dead-bumed and discharged atthe-heated end of the furnace. In

. roasting sulphidic zinc ores from which the zinc is to be recovered by'hydrolysis, it is found that there is a risk-of the finer particles of the ore being over-roasted. In view of this, it was pro- 5 posed to subdivide the ore, before roasting to completion, into particles of different sizes and to treat each grain size in a special furnace throughout, so that. the' maximum roasting speed of each grain size could be taken into conslderation,

The joint heat treatment of fine material comprising dlflferent grain sizes results not merely in the possibility of difference in character between the coarser and finer grains at the completion 15 of the treatment; the finest particles which closely surround the coarser ones, preventuthe access of heat and the reaction gases to the latter. Accordingly, the transformation of the coarser particles is retarded and the furnace output is go correspondingly lowered, Nevertheless, in many instances, the proposal to roast the various grain sizes of fine material separately in difierent furnaces, is rendered impracticable on account of the high prime and running costs of a multiu plicity of furnaces.

According to the present invention, the chemical alteration of fine-grained material that contains a variety of grain sizes at the outset, or

assumes that condition during the treatment, can

be effected by passing the material through a heated, elongated reaction chamberthat is to say, for example, in roasting or calcining, without separating the material into diiferept grain sizes-in such a manner that the several grain I sizes undergo the same chemical transformation with approximately equal completeness. With this object, the finer grain sizes are removedin succession, separately from the coarser sizes, at

two or more points in the elongated reaction chamber, the discharge points being so located that in each case,- the individual grades of grain size are discharged when each grade has under- 4 gone the desired uniform degree of transformation. a The process of the present invention is not comparable with a'known process in which the pulverulent material is introduced at to the top of an upright reaction chamber and subjected to the action of gases ascending from below, in order to effect its chemical transformation. The known process proceeds in such a manner that the reaction takes place when the gases meet the materials in' a. state of suspension, the result being that the materials-insofar as they have taken part in the reaction-become specifically the furnace.

heavier and descend, out of the reaction zone,

. through the reaction chamber, while the untransformed materials, which are specifically lighter than those which have been transformed, are seized upon by an ascending suction current and are drawn in the opposite direction, out of the reaction'zone. Unlike the process of the present invention, this case does not relate to the treatment of substances that are present in different.

grain sizes, or are converted into a variety of grain sizes during the reaction treatment, and

are jointly moved for a considerable distance through a reaction chamber. Consequently, this process is not attended with the drawback that finer materials, in which the reaction is already completed, retard the coarser and not yet transformed materials in their way through the reaction chamber.

In order more fully to explain the invention, the following example is given, referring to-the roasting of pyrites.

The analyses of commercial fine pyrites by screening reveal a remarkable agreement with regard to the percentage proportions of the various grain sizes, the characteristic feature being that by far the greater portion consists of the fine grades of grain size, while the coarser grades are present in merely small amounts.

Fine pyrites with grain sizes between 0 and 8 mm. contain e. g.:

Per cent Grain sizes: 0-2 mm 45-70 2-6 mm 15-30 For the present purpose, it is sufficient to assume a mean composition of:

The examination of the roasted products from such raw fine pyrites shows, in the first place, that in all cases, a decrease in grain size has occurred in all thegrades, that is to say, a percentage increase in the finer grades and a decrease in the coarser grades, has occurred during the treatment. This circumstance is, of course, also borne in mind in devising the roasting process according to the invention, but can be left out of consideration here.

Unroasted pyrites have a mean sulphur content of 47-48%, the roasted products one of 1.5%.

Examination of these products shows that this sulphur content is distributed among the several grain sizes as follows:

According to the present invention, at that point in the furnace at which the roasting of the fine pyrites, grade 0-2 mm. is completed, this grade is removed from the interior of the furnace while the 2-8 mm. grade is left in the fur-" nace for roasting. It has been ascertained that the sulphur content of the 0-2 mm. grade has been reduced to 0.6% by the time the charge has completed half the distance it has to travel through On this occount, an outlet with a screening device in direct connection with the furnace, is provided at this point, and the material corresponding to this grain size is discharged.

Since, for economic reason, a sulphur content of 1.5% is permissible, in the example under consideration, and the 2-6 mm. grade still contains 1.4% of sulphur at the end of the roasting, this product also can be regarded as sufficiently desulphurized and removed, as finished roasted material at a suitable point (for example at 3, Fig. 1) On the other hand, the 6-8 mm. grade contains more than the permissible limit of sulphur. Consequently, this coarse grade which still fails to exhibit adequate roasting, is not regarded as a finished product and according to the invention, is recharged by means of suitable appliances, into the same roasting furnace for the purpose of increasing its travel and therefore the duration of the roasting treatment.

The screening outlet naturally varies in design according to thetype of the furnace. In the case of multi-stage furn aces, an entire stage for example, may be arranged as a screen or segmental screens can be disposed in suitable hearth openings in a stage. Rotary-tube furnaces afford specially suitable conditions. 1

In order more clearlyto understand the invention, reference is made to the accompanying drawings, which illustrate diagrammatically and by way of example different forms of execution of the invention.

Fig. l is a longitudinal vertical section of a rotary furnace embodying the features of the invention;

Fig. 2 is a section on line AB of Fig. 1;

Fig. 3 shows a special form of construction of a screening and discharge device that can be used instead of that shown in Fig.2;

I Fig. 4 is a development of the screen I2 01'. Fig. 3;

Fig. 5 represents a rotary furnace provided with means for returning roasted material from the discharge end of the furnace" to other parts of the furnace that are located nearer the admis sion end of the same;

Fig. 6 is a fragmnetary sectional elevation of a rotary-tube furnace illustrating a further modi- I shown in Fig. 1.

The furnace (Fig. 1) is provided about onethird. the way along, with the first discharge opening I, the second openings 2 being disposed about midway along the furnace and other openings 3 and 4 at the end. In order to prevent any undesired access of air, the discharge openings are fitted with discharging devices 5, 6, 1 and 8, whose structure is more clearly shown in Figs. 2, 3 and 8. By the employment of these devices solids may be removed from the furnace without material admission of air at the discharge points. The screens at the discharge openings may be arranged in various ways. At the first openings I and 2, screens Ia, 211, respectively, are interposed between the shell of the furnace and the discharging devices. At the dischargeppening 3, the screen takes the form of a cylinder I I, situated inside the furnace, the charge material passing over it on the way to the last discharge opening 4. None of the charge material except such as has passed through the screen II can reach the discharge device I. This manner of arranging the screens comes under consideration especially in where or dur g which, a smaller liberation of heat has to be reckoned with. .Inl'lg.2the dischargemeansisshownas embodying a plurality of discharge openings distributed over the perimeter of the furnace and provided with screens and with a single discharging device.

As shown, a plurality of openings 2, 2, 2 are located about the periphery of the furnace, comto municating with a conduit I! which encircles at least the major portion of the circumference of the furnace in the plane of the openings. Secured to this conduit and communicating therewith is the discharge means for ejecting solids without admitting a substantial amount of outside atmosphere to the structure. At the mouth of each of the openings 2, 2, 2 is positioned a screen In adapted for retaining larger pieces of charge while passing smaller pieces. With rotation of the furnace,.the smaller pieces of charge which have passed into the conduit I3 through the openings 2, 2, 2 by way of the screens 2a, 2a, 2a. are moved to and discharged by discharge means 0.

As shown in Fig. 8, the casing of the furnace comprises the iron cylinder IO and the masonry II. The screen la covering the opening I is shown as a perforated plate secured by bolts 3i to the cylinder ll. The bolts Ii also secure the discharge chute to the casing of the furnace. The discharge chute comprises a housing 32 and a cell wheel II which is secured to and rotates with a shaft which carries cross arms 35 outside the housing. The va'hes IQ of the cell wheel 33, by contact of their edges with the wall of housing 32, divide the cylindrical space inside the housing into a plurality of cells or compartments each of which is sealed from the others. Upon rotation of the furnace, the arm of the cross-arms 3! then in the proper position strikes against a stop 31 Tcarried .by asgitable support 38 or by a part of the foundationvv of the furnace. Thus a step by step rotation is imparted to the shaft ll and'cell wheel 32, so that the cells as they pass bygthe discharge opening of the housing empty thertltrough, while the cells entering into the range of the charging opening of the housing are filled again. Discharge chutes of this kind are already known per se; they can be used at all the discharge openings 5, 6, I and l of the furnace.

Pig. 3 represents another embodiment of a screening and discharging device. In this case, the material imues through an outlet, ill, and drops, irrespective of grain size, through the wideopen outlet, on-tothe screening jacket l2 surrounding the shell of the furnace. The fine material passes through said screen and falls on to the inner surface of the external casing H, which delivers it to the outlet controlled by the discharge device I. The coarse material remains inside the screen l2 and is raised thereby and dropped back into the furnace through a second opening, II, (shown in dotted lines at the top of Fig. 3) when the said second opening is in top position. Fig. 4- represe'nts a plane projection of the screen l2 of Fig. 3, with the outlet or discharge opening, II, and the return opening, is, into the furnace indicated in broken lines in their rwpectlve positions.

Ill'he rotational movement of the furnace effects the screening of the material that has fallen into the screen l2. The fine material which has passed-through the screen into the external casing II, travels along the latter and is discharged the furnace.

coming within the scope of a discharge opening 5 during a complete revolution will pass through -said opening and out of the furnace, the invention provides inside the furnace and beyond the discharging device, a barrier ring i6 disposed in known manner and of sufllcient height to prevent lo the accumulated material from trickling over it in the course of a revolution. The arrangement is also such that the material in front of the ring issues from the furnace and is returned thereto immediately behind the ring. The arrangement of a channel, formed by two rings, inside the fumace is preferably for practical reasons and is just as effective as a single ring.

Fig. 5 represents an arrangement by means of which the materialeven screened material, if desired-discharged from the end or from any other point of the furnace, can be automatically recharged into an anteriorly situated portion of This arrangement consists of a worm, 39,-for example of rectangularcross section-so disposed as to result in a turning effect in the opposite direction to the rotational direction of the furnace and connected with the i.n terior of the furnace at convenient points, 40, 4| l2. The rotation of the furnace causes the material to travel inside the worm in a direction, in this instance, opposite to that taken by the charge in the furnace, so that by means of the worm, material can be conveyed from a lower part of the furnace to a higher part. The worm, 39, although shown as rectangular, may be of any convenient cross section. It may be constructed of any convenient suitable material, such as iron or other metal, that is not attacked by the material to be treated. A discharge device is shown at 43.

The arrangement can also be applied to cases in which material is to be conveyed from the anterior portion of the furnace to rearward portions of the latter as more fully described with reference to Figs. 6 and "I. In such cases the rotational direction of the arrangement must, of course, be modified accordingly,

The return transport of the coarser material Y screened off at the end of the furnace may be of twofold importance in the process according to the invention. I

In the first place, coarse-grain material, the chemical transformation of "which has not attained the desired degree can be returned, for 55 the purpose of retreatment, to the head end of the furnace, or to any other suitable point, such as the main reaction zone. Under the single or repeated treatment of the coarse-grain material in the furnace, it then acquires the desired char- 00 acter. On the other hand, the return of a portion of the charge material from a cooler into a proposed hotter zone of the furnace, lowers the temperature in said hotter zone. It will be assumed that a certain kind of pyrites g5 attains a permissible roasting temperature of 1000 C. and that the product at the end of the furnace still has a temperature of about 200 C. If now, 20-25% for example, of the roasted product in the cooled condition, be returned to the main reaction zone, this latter will be cooled to the extent of about 200-250 C., that is, to 800-7500. Experience has shown that the efliciency of the furnace depends on the amount of the charge, which is in direct proportion to the 73.

heat liberated by the combustion of the sulphur. Consequently, in the case of the example, the charge of rawpyrites can be increased by the amount required to restore to 1000 C. the temperature of the charge from the 800-750 C. to which it has been lowered.

According to the invention, the screen placed round the furnace shell in Figs. 3 and 4, can be disposed, with equal effect, in the worm passing round the furnace. The discharge openings serving to remove the roasted material from the furnace can also be employed at the same time for the admission of air. In some cases, it is also advisable to connect the outletstogether for example by means of channels or the like arranged as a worm passing around the furnace. The material from several outlets will therefore be then collected and discharged at a single point from the collecting channel which of course, is integrally connected to the furnace. In such case,

the devices required for the reception of the charge from the furnace can be of a substantially simpler character. The channels can be provided with interior classifying screens, so that the material is separated in accordance with-its grain size, during its passage through the channel, as is shown in greater detail in Figs. 6 and 7. This is particularly advisable when. the various grain sizes are to be put to different uses, one grade, the coarse for example, being subjected to a secondary treatment, for example by returning it to the furnace by means of the arrangement shown in Fig. 5, or if the finest screenings are unsuitable for the subsequent further application and are to be transformed into a coarser condition by known processes.

The rotary-tube furnace according to Figs. 6 and 7 has the ordinary charging device H, the furnace casing l8 and the wall I9 and also the gas fine that joins on to the upper end of the furnace. The discharge device 2| for the material treated in the furnace is located at the lower end of the furnace; In addition the furnace is provided with barrier rings 22 and air inlets 23. The rotary crowns are designated by 24, the drive by 25 and the foundation by 26. Between every two barrier rings or directly in front of a barrier ring, openings 21 are provided in the casing of the furnace. These openings communicate with a conduit or passage 28 encircling the furnace casing helically, and divided for a portion of its length by the screens 29 concentric with the furnace. Each screen extends from one opening 21 nearly to one of the return openings 30 in the furnace wall.

The material which has traveled through a part of the furnace, or a portion of this material, falls through the opening 21 and enters the passage 28 and then reaches the screen 29. Onthis screen it is shaken forward due to the rotation of the furnace, the fine material thereby falling through the screen and passing along on the outside wall 28 of the passage to the discharge opening 2|. The portion of the material remaining on the screen passes through the openings 30 back into the furnace. This portion of the material is again treated in the furnace until it reaches another opening 21 being then exposed in the same way and with the same means to a. second and possibly to a third or fourth screening.

It is possible in some instances to provide the screening devices-only'in one part of the furnace, e. g., the upper, or anterior, half, and to use the rest of the furnace for the uninterrupted the present invention. All other kinds of fur- 5 naces in which the material traverses an elongated path during the heat treatment arealso applicable. It is not necessary that the grades of grain size that are successively removed from the furnace should be the same in all cases.10.

Both these grades and the screening devices serving for their removal may be adapted to a far reaching extent to the reaction conditions prevailing in the furnace, especially as regards temperature. Nevertheless, it is possible in all cases 15 to distribute the several points of discharge on the perimeter of the furnace in such a manner that" the discharged portions have all undergone the same chemical transformation.

This is a division of my application Serial No. 20 687,234, filed August 28, 1933.

I claim:

1. In a rotary-tube furnace provided upon its interior with barrier rings, discharge openings distributed throughout its length, each of said 25;

openings lying adjacent at least one barrier ring and being provided with screening means partially encircling the furnace, the screening means being positioned within a conduitdisposed between several of said dischargeopenings.

2. A rotary-tube furnace according to claim 1, characterized in that the connecting conduit is adapted to lead screenings from a plurality of the discharge openings jointly out of the furnace.

3. A rotary-tube furnace according to claim 1, characterized in that the furnace is provided, intermediate its ends, with at least one opening providing communication between the-screening means and the interior of the furnace and functioning to return to the furnace material incao pable of passing through the screening means.

4. A rotary-tube furnace according to claim 1, characterized in that the furnace is provided, intermediate its ends, with openings pro'viding communication between the screening means and the interior of the furnace, said openings functioning to return to the furnace material incapable of passing through the screening means, such return openings being one less in number than said discharge openings-so that there is a return opening complemental to each of the discharge openings except the last, said connecting conduit being adapted to discharge screenings of the furnace charge from a plurality of the discharge openings jointly.

5. A rotary-tube furnace according to claim 1, characterized in thatat least one of the discharge openings lies between two adjacent barrier rings on the interior surface of the furnace.

6. In a rotary-tube furnace provided upon its interior with barrier rings, screening means including a screen for treating the furnace charge,

a plurality of discharge openings each lying adjacent at least one barrier ring of the furnace and adapted to discharge material from the furnace onto the screen of said screening means, and means associated with said screening means for takingoif screened material from the furnace.

7. In a rotary-tube furnace provided upon its interior with barrier rings, screening means including a channel member and a screen for treating the furnace charge, a plurality of discharge openings each lying adjacent at least one barrier ring of the furnace and adapted to discharge material from the furnace onto the screen 76 of said screening means and within said channel 8.1 rotary-tube furnace as in claim 6, in which member, said channel member encircling the each discharge opening except the last is profurnace and providing means for discharging vided with a separate screen. screened material and for returning to the iur- 5 nace oversize material which will .notpass said CARL PAUL DEBUCH. 5

screen. v

CERTIFICATE OF CORRECTION.

Patent No. 2,019,597. v 1 October 29, 1955.

CARL PAUL DEBU H.

"It is hereby certified that error appears" in the printed specification of the above numbered patent requiring correction as follows: Page 2, first oclumn, line 68, after "for'! insert further; and line '72, for 'occount" read Y account; second column, line 45, fc-r- "'fragmnetary" read fragmentary; page 3, l second column, line 17, for "preferably" read preferable; and that" the said Letters Patent should be read with these corrections therein that the same may confoFm to the record of the case in the Patent pffioe.

Signed and sealed this 4th day of February, A. D. 1956.

Leslie Frazer (Seal) Acting Commissioner of- Patents;

of said screening means and within said channel 8.1 rotary-tube furnace as in claim 6, in which member, said channel member encircling the each discharge opening except the last is profurnace and providing means for discharging vided with a separate screen. screened material and for returning to the iur- 5 nace oversize material which will .notpass said CARL PAUL DEBUCH. 5

screen. v

CERTIFICATE OF CORRECTION.

Patent No. 2,019,597. v 1 October 29, 1955.

CARL PAUL DEBU H.

"It is hereby certified that error appears" in the printed specification of the above numbered patent requiring correction as follows: Page 2, first oclumn, line 68, after "for'! insert further; and line '72, for 'occount" read Y account; second column, line 45, fc-r- "'fragmnetary" read fragmentary; page 3, l second column, line 17, for "preferably" read preferable; and that" the said Letters Patent should be read with these corrections therein that the same may confoFm to the record of the case in the Patent pffioe.

Signed and sealed this 4th day of February, A. D. 1956.

Leslie Frazer (Seal) Acting Commissioner of- Patents; 

